HAMDEN -- With a face that only a mother could love and a mating call from a dark nightmare, one might think that the 17-year cicada, set to appear in a few weeks, might not have too many fans.

But scores of people across the state are anxiously awaiting the thumb-sized insect, which experts say has seen its numbers decline in the last two centuries.

"They've been disappearing, especially from the northern end of their traditional range," said Chris Simon, professor of ecology and evolutionary biology at the University of Connecticut. "You don't see them in Massachusetts anymore."

Worldwide, there are about 3,000 cicada species and all spend years underground as juveniles. It's the 17-year cicada that reaps special interest because of its ability to stage a synchronized emergence after many years; this will take place this year in Connecticut between late May and mid-June, said Chris T. Maier, an entomologist with the Connecticut Agricultural Experiment Station.

The ones that will emerge in 2013 belong to Brood II. All live in the U.S. in a narrow swath that extends roughly from Massachusetts to Georgia. In Connecticut, you're most likely to encounter them in a footprint that includes just 22 municipalities in central to south-central Connecticut, extending roughly from Farmington south to the shoreline towns from East Haven to Madison, Maier said.

"It has a restricted distributed range in Connecticut," he said. "In fact, I will be documenting the locations of populations in Connecticut to see how they're faring because DEEP (the state Department of Energy and Environmental Protection) is interested in the decline of the cicada population."

There used to be another brood of 17-year cicada years ago, but it's no longer seen here, she said.

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Declining numbers are bad news for the periodic cicadas because their reproduction strategy relies on what experts call "predator satiation," which is producing more than enough individuals to satisfy their predators. Cicadas are large, lumbering insects and they don't pose much of a challenge for birds or anything else that wants an easy treat.

"The rise of the farms really knocked them back," she said, "and they never recovered. Even the reforestation of the state in the 20th century didn't help because the ground was disturbed."

Magicicada adults -- that's the genus that comprises Brood II -- have black bodies and striking red eyes and orange wing veins, with a black "W" near the tips of the forewings. Most emerge in May and June. Don't confuse them with the so-called dog-day cicada, Tibicen canicularis, which appears every year, although scientists say that they likely spend a few years underground, too.

Cooley said that it's still difficult to gauge the degree of periodic cicada decline. When Brood II emerges this year, a far more exhaustive effort will be undertaken to determine their numbers, providing a better baseline for when they're due to appear again in 2030.

Entomologists won't mind if you call them "bugs," because they belong to the Hemiptera order of insects, also known as the "true bugs." Their mouth parts are modified into a structure known as a rostrum, used for sucking fluids, usually sap from plants, and many of these cause great economic hardship to farmers. The 17-year cicada is seen as beneficial, however, as their years feeding off root sap are easily shrugged off by trees. Certainly songbirds won't mind being surrounded by thousands of the juicy, sluggish insects.

As with scores of other animals and plants, the cicada is sensitive to habitat loss.

"They're certainly one of the most remarkable insects in the entire world," Maier said. "They can synchronize their reproductive cycles every 17 years. These are mass emergences. Then you have their big chorusing centers where you can have thousands of males singing in the same tree."

Maier studied that last two broods, in 1979 and 1996, and determined that the adults will begin reproductive behavior three weeks after crawling out of the soil.

They look like something out of a 1950s science fiction movie. A few days before emerging, the nymph's eyes turn from white to red. They crawl up a tree and molt into the adult stage, their cream-colored exoskeleton turning black. Their translucent wings, which can barely get the heavy animals airborne, are laced with copper-colored veins.

Even in the strange world in insects, the 17-year cicada is something of an oddball. Its antennae are positioned in front of those red eyes and there are three more tiny red eyes on its forehead.

Another odd characteristic is the way they produce their unearthly mating call, sometimes described as the landing of a flying saucer from another planet.

Most musical insects, like crickets, produce sound by rubbing together two body parts. Not so with cicadas, which make a racket using a pair of abdominal structures called "tymbals." They have their own system of muscles and produce noise by buckling, much like a child's click toy, only operating hundreds of times a second.

Only the males can sing, and do so only to attract a female. Males congregate by the thousands "producing a clamor not soon to be forgotten," Meier said.

After copulation, females lay about 400 eggs in pencil-sized twigs. The newborn nymphs emerge after a few weeks, then drop to the ground and burrow into the soil to start the cycle again.

Simon said that if you find a cicada that you think belongs to Brood II, take a picture of it and send it to the experts by visiting the website, www. magicicada.org.